Why Air Travel Can Take a Bigger Toll on the Brain Than We Realize

Deborah Kan is an award-winning journalist and founder of Being Patient. In this “Thought of the Week” column each Friday, she highlights one of the key stories shaping the future of brain science.

Dear readers.

I spent last week in Hong Kong, but when I landed in San Francisco, I was overcome with a splitting headache. I’ve flown to Asia and back more times than I can count but wondered why flying gives me a bad headache on some flights but not others.  

I did a bit of research and discovered that the cabin you’re sitting in isn’t pressurized to sea level. It’s pressurized to the equivalent of 6,000 to 8,000 feet above sea level (about the height of Machu Picchu.) That means every passenger on a long-haul flight is spending 14 hours in conditions similar to the base camps of high-altitude mountaineers. And one part of the brain takes the hardest hit.

The region of the brain most affected by flying is the prefrontal cortex. Attention, learning, verbal abilities, and executive function all decline to variable degrees with ascent to altitude. Past studies documented this with handwriting samples, which became more jumbled as altitude increased. The prefrontal cortex is the last part of the brain to develop in adolescence. It appears to be among the first to register the effects of reduced oxygen. 

Cabin air humidity can drop to 10 to 20 percent, compared to 30 to 60 percent on the ground. The brain is nearly 75 percent water, and even mild dehydration measurably impairs cognitive function. Alcohol makes it worse. At altitude, the body absorbs alcohol faster than it does at sea level, which means one drink at 37,000 feet is more like two on the ground!

A neuroimaging study published in Human Brain Mapping found that functional activity was significantly reduced in the hippocampus following long-haul flights crossing multiple time zones. The hippocampus is the part of the brain where memories are made and stored. Researchers from UC Berkeley found that jet lag directly reduces the birth of new neurons in the hippocampus. And the effects don’t resolve quickly. Cognitive function was impaired not just during jet lag but for up to a month afterward!

For frequent long-haul flyers, the picture becomes more concerning. Studies on flight attendants who experienced repeated jet lag with limited recovery time between flights showed reduced temporal lobe volume and spatial learning deficits compared to ground crew. These cognitive deficits were long-lasting, extending for several years, and were associated with elevated levels of cortisol, the stress hormone. Cortisol, when chronically elevated, is specifically disruptive to hippocampal function. 

So, headache explained! I went down a rabbit hole, but there’s enough research to understand the next time I fly long haul, hydration and sleep are the best ways to make a full recovery.

With hope,
Deborah